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phpSysInfo Multiple Vulnerabilities (HTTP_ACCEPT_LANGUAGE, sensor_program,
VERSION, charset)
------------------------------------------------------------------------
SUMMARY
<http://phpsysinfo.sourceforge.net/> phpSysInfo is a PHP script that
displays information about the host being accessed. It will displays
things like Uptime, CPU, Memory, SCSI, IDE, PCI, Ethernet, Floppy, and
Video Information. A number of holes - all of them attributed to a rather
crude (and unneeded) register_globals emulation - allow for arbitrary file
inclusion, amongst other things.
Multiple vulnerabilities have been discovered in phpSysInfo allowing
attackers to cause the program to reveal sensitive files and include
arbitrary HTML and/or JavaScript.
DETAILS
It is important to note that due to the nature of phpSysInfo, it is
unlikely to be run inside an open_basedir, since most of the information
the software obtains is from the /proc or /etc directories. Furthermore,
few administrators will restrict its access to PHP's shell functions,
since a such restriction would render the software unusable. In fact, the
author requires that safe_mode be set to Off and no other restrictions be
imposed on the PHP installation.
A hole that was reported in CVE-2003-0536 and is reported as "fixed" in
the phpSysInfo README still persists. The reason for this problem lies in
the incorrect handling of variables by the "globalization layer"
implemented in phpSysInfo's index.php - quote:
if (!empty($HTTP_GET_VARS)) while (list($name, $value) =
each($HTTP_GET_VARS)) $$name = $value;
if (!empty($HTTP_POST_VARS)) while (list($name, $value) =
each($HTTP_POST_VARS)) $$name = $value;
As the interested reader will easily see, this two-liner overwrites the
complete scope, including the superglobal variable $_SERVER. By injecting
a local path name into $_SERVER['HTTP_ACCEPT_LANGUAGE'], an attacker can
now include arbitrary files. If they have a way to create content on the
target server (such as an entry in syslog or the web server log file),
they can use this to execute arbitrary code.
In the Debian Sarge package, injecting only HTTP_ACCEPT_LANGUAGE is
sufficient - the current source tree (phpsysinfo-dev from sf.net) requires
the attacker to additionally inject the $lng parameter.
Example:
/index.php?_SERVER[HTTP_ACCEPT_LANGUAGE]=../../README%00
/index.php?_SERVER[HTTP_ACCEPT_LANGUAGE]=../../README%00&
lng=../../README%00
The variable $sensor_program is set in config.php, but can be overwritten
since config.php is actually included *before* reglobalization takes
place. With this variable, arbitrary file inclusion is possible on some
platforms, dependant on the local realpath() implementation.
Example:
/index.php?sensor_program=lmsensors.inc.php/../../README%00
Additionally, $sensor_program can *still* be used to inject active
contents into the page, known as Cross-Site Scripting. This issue was
discussed in CVE-2005-0870 and still exists. The other XSS holes mentioned
in that ad- visory are still valid, too. They can be abused with
register_globals Off, this is different from the advisory by ISS. It is,
however, not exploitable on Debian systems.
An additional attack vector for Cross-Site Scripting attacks is the
variable $VERSION, which is used for the version string displayed on the
bottom of each page.
Example:
/index.php?VERSION=%22%3E%3Cscript%3Ealert('xss')%3C/script%3E
A fairly unknown attack class is so-called HTTP Response Splitting, an
attack that allows for "selective defacement" of web pages by poisoning
forwarding or reverse proxies. An explanation of this attack class is
beyond the scope of this advisory.
Using HTTP Response Splitting, arbitrary strings can be injected into the
variable $charset, which is meant to include a value such as "iso-8859-1"
or similar, but is only set to a value inside a language include file if a
language in fact requires a character set different from iso-8859-1. In
all other cases, it can be set via the URL. This variable is fed to a
header() call without any additional checks. By breaking up the argument
with \r\n, the attacker can inject a complete second HTTP response. This
response is the only one that will be returned by any intermediate proxy,
showing whatever HTML the attacker injected previously.
Example:
/index.php?charset=%0d%0aContent-Length:%200%0d%0a%0d%0aHTTP/1.1 200
OK%0d%0aContent-Type: text/html%0d%0aContent-Length:
19%0d%0a%0d%0a<html>Hacked!</html>
This example will print out a simple (and invalid) HTML page containing
only the string "Hacked!" if the victim accesses the phpSysInfo instance
from behind a proxy. Direct access will probably yield an empty page,
since many browsers do not know how to handle more than one response to a
HTTP request.
Disclosure Timeline:
10. November 2005 - Bug disclosed to vendor.
10. November 2005 - Updated version 2.4 released.
11. November 2005 - 2.4 does not seem to fix - own patch sent to vendor.
12. November 2005 - New updated version 2.4.1 fixes the issues.
13. November 2005 - Public disclosure.
Recommendation:
We have provided a bugfix to the vendor, which, in addition to their own
fix, will be included in version 2.4.1 of phpSysInfo. We also recommend
installing the Hardening Patch for PHP which would have mitigated the
response splitting problem (by not allowing multiline headers) and the
$_SERVER overwriting issues (by not allowing certain superglobals to be
overwritten from the outside). If you want to fix the issue yourself, just
comment out the lines mentioned in an earlier paragraph of this advisory
and selectively infer the variables $_REQUEST['lng'] and
$_REQUEST['template'] from the outside.
Additionally, access to the includes/ directory should be restricted by
appropriate means, e.g. a .htaccess file.
CVE Information:
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2005-3347>
CVE-2005-3347
<http://www.cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2005-3348>
CVE-2005-3348
ADDITIONAL INFORMATION
The information has been provided by
<mailto:christopher.kunz@hardened-php.net> Christopher Kunz.
The original article can be found at:
<http://www.hardened-php.net/advisory_212005.81.html>
http://www.hardened-php.net/advisory_212005.81.html
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